Main Article: Openbook
This hashtag indicates that the post is related to Openbook.
This does not relate to the content on Openbook. It is primarily used to indicate when a post is talking about how the website functions, which is a combination of the software behind Openbook and the culture of the website which utilizes that software.
The #openbook tag might also be used in conjunction with #bugreport to report when a software bug is found on Openbook.
See Also: hashtag combos, #openbook101